Electronically Controllable Resistor

ABSTRACT

An electronically controllable resistor (ECR) designed for changing the resistance of a portion of a circuit comprises a voltage converter, a subtractor, an instrumental resistor (IR), and an executive element (EE) which can include at least one MOSFET or IGBT or a vacuum tube. There are a high-potential and two control voltage sources. The converter, which can use logarithmic amplifiers or be digital, is adapted to multiply the high-potential voltage by one of the control voltages and divide by another one. The resulting intermediate voltage is applied to the subtractor and compared therein with a voltage drop on the IR created by the current flowing through the IR and the EE. Thus, the ECR resistance can be regulated. The ECR makes it possible to achieve a wide range of resistance values, down to ultra-small values, while maintaining tolerance to destabilizing factors, including temperature. Also claimed is an ECR control circuit.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to electrical engineering and electronicsand is intended to control changes of resistance of a portion of anelectric circuit using electronic means.

2. Description of Related Art

Known in the art have been means to electronically control resistance ofa portion of an electric circuit with the use of voltage controllablevariable resistors. One of those designs, specifically, anelectronically controllable resistor (ECR) including a field effecttransistor (FET) is described in Electronic Circuits: Handbook forDesign and Application, by U. Tietze et al., Springer, 1978, FIG. 5.19.Controlling voltage is applied directly to an input of the ECRrepresented by the gate of a FET. As the controlling voltage varies, sodoes the resistance of the FET channel. In this way, control ofresistance of a portion of an electric circuit (and, consequently,control of voltage, current and power of wanted electrical signalstherein) is carried out.

A common feature of this design and the present invention is a MOSFETwith three terminals.

Disadvantages of the known solution are: a narrow range of voltagesbetween the source and drain of the FET where an approximately lineardependence between the controlling voltage and resistance of theelectronically controllable resistor ECR (namely, the resistance of theFET channel) is observed; spread in values of control characteristicswhich does not make it possible to achieve sufficient accuracy ofsetting a resistor value; temperature dependence of controlcharacteristics which does not allow to have stable characteristicsacross a temperature range;

dependence of resistor values from the voltage between the source anddrain of the FET.

Also known (from the Russian patent RU2658681, G05F 1/59, publ. Jun. 26,2018) has been a design where an ECR comprises a MOS-transistor, aresistor of the rate of R_(br) connected in parallel to theMOS-transistor and being bridged thereby, a controlling voltageconverter, and a subtractor.

As the controlling voltage changes, so does the resistance of theMOS-transistor channel and, accordingly, the resistance of the ECR (fromR_(br) when the MOS-transistor is closed to practically zero when theMOS-transistor is completely open). Due to that, controlling of theresistance of a portion of an electrical circuit takes place.

Common features of the proposed design and the prior art are:

-   -   a converter of controlling voltage;    -   a subtractor;    -   a MOS-transistor with three terminals, the gate of the        transistor being connected to an output of the subtractor.

The prior art apparatus appears to suffer from insufficient accuracy ofcontrolling resistance of a portion of an electric circuit, especiallywhere affected by destabilizing factors, such as ambient temperature.

An apparatus disclosed in the Soviet inventor's certificate SU1807554,H03G 3/30, publ. Apr. 7, 1993, is believed to be the closest analog(prototype) of the present invention.

The prototype includes an ECR comprising two reference resistors and twoprecision multipliers, to thus enhance the precision of setting a givenvalue of resistance. A chip 525ΠC3 or its analogs, such as AD534, isused in the apparatus as a precision analog multiplier functioning as avoltage converter. The resistance of the ECR is proportional to apreferred value of the reference resistor, which acts as an instrumentresistor, and can vary in reverse proportion to a change of controllingvoltage at an input of the voltage converter.

Common features of the prototype and the proposed design are:

-   -   terminals for connecting to a first source of controlling        voltage and to a common wire, as well as a high-potential and a        low-potential terminals for connecting the ECR to an electric        circuit;    -   a voltage converter, whose first input is connected to the        terminal of the ECR to be connected to the source of first        controlling voltage, and whose third input is connected to the        high-potential terminal of the ECR;    -   a subtractor;    -   an instrument resistor;    -   a connection of one of inputs of the subtractor to an output of        the voltage converter;    -   a connection of the other input of the subtractor to a first        terminal of the instrument resistor;    -   a connection of the low-potential terminal of the ECR to the        terminal for connecting to the common wire

In the prototype, however, the current via the instrument resistor flowsto the common wire through the limiting resistor (in accordance to the525ΠC3 or, what is the same, to AD534). In real practice, consequently,there exists a dependence of the resistance of the electronicallycontrollable resistor on the resistance of the limiting resistor, andneglecting this component is only possible where the value of theinstrument resistor is many times that of the limiting resistor.Therefore, it is impossible in the prototype to achieve sufficiently lowresistance of the ECR frequently needed in real practice. Additionally,achieving small values of the ECR resistance is limited by the reversedependence thereof from the controlling voltage, so as to provide smallvalues of the resistance, the controlling voltage should be as big asimpractical. On the other hand, it is impossible in the prototype tohave a direct dependence of the resistance from the controlling voltage.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome disadvantages of theprior art by providing a preferably low-ohmic ECR enabling fine settingof the desired resistance value while maintaining tolerance todestabilizing factors including temperature changes over wide range.

The technical result, believed impossible to be achieved in prior art,lies in widening the range of values of the rated resistance of the ECR,mainly to the side of small values thereof. The value of the resistanceof the portion of the electric circuit where the ECR is placed can be aslow as possible, with the technical implementation in view, while hightolerance to destabilizing factors is maintained.

The ECR according to the present invention is provided with a terminalfor connecting to a first source of controlling voltage, with a terminalfor connecting to a common wire, and with a high-potential terminal anda low-potential terminal for incorporating the ECR into an electriccircuit. The ECR comprises a voltage converter, an instrument resistor,and a subtractor. The voltage converter has three inputs. A first inputis connected to the terminal for connecting to a first source ofcontrolling voltage, and a third input is connected to thehigh-potential terminal of the ECR. A first input of the subtractor isconnected to an output of the voltage converter, a second input of thesubtractor is connected to a first terminal of the instrument resistor,and the low-potential terminal is connected to the terminal forconnecting to a common wire,

The above object is achieved in this ECR by providing same with anexecutive element and with an additional terminal for connecting to asecond source of controlling voltage. A first terminal of the executiveelement is connected to the first terminal of the instrument resistor, asecond terminal of the executive element is connected to an output ofthe subtractor, and a third terminal of the executive element isconnected to the high potential terminal. A second terminal of theinstrument resistor is connected to the low-potential terminal, and asecond input of the voltage converter is connected to the additionalterminal for connecting to a second source of controlling voltage.

An additional feature of the present ECR is that the voltage converteris adapted to multiply voltage at the high-potential terminal by aquotient of a value of one of the controlling voltages by a value ofanother of the controlling voltages.

Yet another feature of the proposed ECR is that the voltage convertercan include three logarithmators, parallel to each other, an adder, anadditional subtractor, and an input of a first of the threelogarithmators is connected to the high-potential terminal, an input ofa second of the three logarithmators is connected to the source of oneof the controlling voltages, an input of a third of the threelogarithmators is connected to the source of another of the controllingvoltages, outputs of the first and second logarithmators are connectedto inputs of the adder, an output of the adder is connected to anon-inverting input of the additional subtractor, an output of the thirdlogarithmator is connected to an inverting input of the additionalsubtractor, an output of the additional subtractor is connected to aninput of the exponential converter, and an output of the exponentialconverter is the output of the voltage converter.

Still another feature of the invention lies in that the voltageconverter comprises a digital computing unit, an analog-to-digitalconverter, and a digital-to-analog converter. An input of theanalog-to-digital converter is connected to the third input of thevoltage converter, an output of the analog-to-digital converter isconnected to one input of the digital computing unit, whereas anotherinput of the digital computing unit is connected to the second input ofthe voltage converter. An output of the digital computing unit isconnected to an input of the digital-to-analog converter, and an outputof the digital-to-analog converter is connected to the output of thevoltage converter. The first input of the voltage converter includes anat least single-bit digital data bus connected to the terminal of theelectronically controllable resistor for connecting to the first sourceof controlling voltage, and the third input of the voltage converterincludes an at least single-bit digital data bus connected to theterminal of the electronically controllable resistor for connecting tothe second source of controlling voltage.

Also, the executive element of the electronically controllable resistorcan include at least one FET, particularly MOSFET.

Alternatively, the executive element of the electronically controllableresistor can include at least one bipolar transistor, particularlyinsulated-gate bipolar transistor.

Further alternatively, the executive element of the electronicallycontrollable resistor can include at least one electronic tube.

The above-described design makes it possible to use the proposed ECRresistor in apparatuses where it is required to control resistance basedon both—direct or inverse dependence from controlling voltage, as wellas based on the dependence from both variable controlling voltages.Also, due to using executive element that can pass large current, itbecomes possible to obtain not only large preferred values of theinstrument resistor, as in the prototype, but also small preferredvalues of the instrument resistor and, consequently, of the ECR.

BRIEF DESCRIPTION OF DRAWINGS

The essence of the proposed design is further explained with referenceto accompanying drawings, where

FIG. 1 presents one of possible variants of an analog implementation ofthe electronically controllable resistor according to the presentinvention;

FIG. 2 illustrates one of possible variants of a digital implementationof the electronically controllable resistor according to the presentinvention;

FIGS. 3 and 4 show modifications of the electronically controllableresistor shown, respectively, in FIGS. 1 and 2;

FIG. 5 illustrates resistance of the electronically controllableresistor versus controlling voltage response characteristic;

FIG. 6 shows one of possible implementations of a voltage converter; and

FIG. 7 shows another one of possible implementations of a voltageconverter.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of better understanding of the present invention, thefollowing definitions are introduced.

Voltage converter—a component of an electric circuit adapted to convertcontrolling voltages into an intermediate signal, the value of theintermediate signal being able to be set equivalent (equal) to a setratio of signals from sources of controlling voltages. The voltageconverter can have various implementations, including, but not limitedto, analog IC, microprocessors, programmed logic arrays, etc.

Executive element—a component of an electric circuit provided with threeterminals, one of the terminals being a control input. The executiveelement can have various implementations, including, but not limited to,those using MOS transistors, bipolar transistors (including those withinsulated gate), electronic tubes, etc.

Presented in FIGS. 1 and 2 is an electronically controllable resistor(ECR) 1 comprising a voltage converter 101, a subtractor 103 (including,for example, an operational amplifier), an instrument resistor 105, andan executive element 107. A first and a second inputs 109 and 111 of thevoltage converter 101 are connected, respectively, to terminals 104 and106 of the ECR 1 meant for being connected to a first and a secondsources of controlling voltages (not shown). A third input 113 isconnected to a high-potential terminal 10 of the ECR 1, and an output115 of the converter 101 serves for supplying an intermediate signal tothe subtractor 103. Power supply voltage comes to a terminal 102 of theECR 1, whereas a terminal 108 is connected to a common wire. A first(non-inverting) input 117 of the subtractor 103 is connected to theoutput 115 of the voltage converter 101, a second (inverting) input 119of the subtractor 103 is connected to a first terminal 121 of theinstrument resistor 105, and an output 123 of the subtractor 103 servesto supply a control signal to the executive element 107 having, forexample, three terminals. A first terminal 125 of the executive element107 is connected, for example, to the first terminal of the instrumentresistor 105, a second terminal 127, which is a control input of theexecutive element 107, is connected to the output 123 of the subtractor103, whereas a third terminal 129 of the executive element 107 isconnected, for example, to the high-potential terminal 10 of the ECR 1.

Also, a second terminal 131 of the instrument resistor 105 is connectedto a low-potential terminal 12 and to the terminal 108 of the ECR 1. Thehigh-potential, 10, and low-potential, 12, terminals serve to connectthe ECR 1 into an electric circuit (not shown).

In a digital implementation (FIG. 2), ECR 2 comprises voltage converter201 which, in turn, comprises an analog-to-digital converter 233, adigital computing unit 235, and a digital-to-analog converter 237. Aninput of the analog-to-digital converter 233 is connected to a terminal213 of the voltage converter 201. Coming to inputs of the digitalcomputing unit 235 are controlling voltages in a digital form from theinputs 209 and 211 of the voltage converter 201 and a signal from anoutput of the analog-to-digital converter 233. The digital-to-digitalconverter 237 is connected by an input thereof to an output of thedigital computing unit 235 and by an output thereof to an output 215 ofthe voltage converter 201.

The ECR designed in the above-discussed manner makes it possible to havecontrolled resistance of the ECR (between the high-potential andlow-potential terminals thereof) which varies according to the followingrelation:

R ₀ =U _(C1) *R/U _(C2)  (1),

i.e. the value R₀ of the resistance of the ECR is proportional to thepreferred value R of the instrument resistor connected in series to theexecutive element, the proportionality factor being equal to quotient ofthe value U_(C1) of the first controlling voltage to the value U_(C2) ofthe second controlling voltage. Due to that, the proposed ECR can beemployed not only in apparatuses where resistance should be controlledfollowing a direct dependence thereof from the controlling voltage, butalso where the dependence is inverse or where dependence from bothvariable controlling voltages takes place.

As distinct from the prototype, where only large preferred values of theinstrument resistor can be obtained, the proposed ECR can, due to usingthe executive element that can pass big currents therethrough, obtainalso small preferred values of the instrument resistor and,consequently, small values of resistance of the ECR.

According to FIG. 1, the ECR 1 operates as follows. Power supply voltageU_(CC) is applied to terminals 102 and 108 of the ECR 1 and the first,U_(C1), and second, U_(C2), controlling voltages are applied toterminals 104 and 106 of the ECR 1 and, respectively to the inputs 109and 111 of the voltage converter 101. Coming at the same time to thethird input 113 of the voltage converter 101 from the high-potentialterminal 10 of the ECR 1 is voltage U₁ corresponding to the potentialdifference between the high-potential, 10, and low-potential, 12,terminals of the ECR 1.

The voltage converter 101 converts the voltages U_(C1), U_(C2), and U₁in such a way that being formed at the output 115 of the voltageconverter 101 is an intermediate signal S having value equal to theproduct of the voltage U₁ at the high-potential terminal 10 of the ECR 1by the quotient of the value of one controlling voltage, for example,the second one, by another controlling voltage, for example, the firstone. The signal is illustrated by the relation:

S=U ₁ *U _(C2) /U _(C1)  (2).

The voltage converter 101 can be realized in any known way, and, forexample, according to the design described inelectrono.ru/4-1-analogovyy-peremnozhitel-signalov-micrshema.

Particularly, it is possible to implement the converter 101 usinglogarithmation and exponential (inverse) conversion and respectiveschematics shown in FIG. 6. There, 601, 602, and 603—logarithmatorsperforming conversion U_(out)=Ln (U_(in)), where U_(out) and U_(in) are,respectively, output and input voltage of the logarithmators; 604—anadder realizing function U_(out)=U_(in1)+U_(in2); 605 is an additionalsubtractor performing function U_(out)=U_(in1)−U_(in2) where U_(in1) andU_(in2) are, respectively, signals at the non-inverting and invertinginputs of the subtractor 605; and 606 is an exponential convertercarrying out function U_(out)=exp (U_(in)).

With accepted designations in view, the voltage converter 101 operatesas follows.

The controlling voltages U_(C1) and U_(C2) come to inputs oflogarithmators 601 and 602, respectively, and the voltage U₁ from thehigh-potential terminal 10 of the ECR 1 comes through the third input113 of the voltage converter 101 to an input of the logarithmators 603.In consequence of logarithmic conversion, a signal Ln (U_(C1)) isgenerated from an output of the logarithmator 601, a signal Ln (U_(C2))is generated from an output of the logarithmator 602, and a signal Ln(U₁) is generated from an output of the logarithmator 603. Thelogarithms of the input signals obtained in such a way are applied froman output of the logarithmator 601 to an inverting input of theadditional subtractor 605, and from outputs of the logarithmators 602and 603, via the adder 604, to a non-inverting input of the additionalsubtractor 605. Due to that, a signal Ln (U₁)+Ln (U_(C2))−Ln (U_(C1)) isgenerated at an output of the additional subtractor 605. Afterconversion in the exponential converter 606, a signal is generated at anoutput thereof, the signal being the output signal of the voltageconverter 101:

S=U ₁ *U _(C2) /U _(C1)  (2).

The intermediate signal formed in the above manner comes from the output115 of the voltage converter 101 to the first, non-inverting, input 117of the subtractor 103 and coming to the second, inverting, input 119 ofthe subtractor 103 from the first terminal 121 of the instrumentresistor 105 is voltage U₂. The value of U₂ is equal to the drop involtage across the resistor 105 caused by current I₀ of the executiveelement 107. The I₀ flows, due to the potential difference U₁ betweenthe high-potential, 10, and low-potential, 12, terminals of the ECR 1,in the following circuit: the high-potential terminal 10—the executiveelement 107—the instrument resistor 107 connected in series with theexecutive element 107—the low-potential terminal 12.

Consequently, the value of the voltage U₂ is expressed by the relation:

U ₂ =I ₀ *R  (3),

where R is the preferred value of the instrument resistor, which valuecan be chosen as small as possible with the technical implementation inview.

Applied from the output 123 of the subtractor 103 to the control inputof the executive element 107 is the voltage proportional to thedifference between the intermediate signal S at the first,non-inverting, input 117 of the subtractor 103 and the voltage U₂ at thesecond, inverting, input 119 of the subtractor 103. If the value of theintermediate signal S is larger than the value of the voltage U₂, thenthe voltage at the control terminal 127 of the executive element 107opens the executive element 107, current I₀ through same increases,resulting in the increase of the voltage U₂. This process will continueuntil the value of the voltage U₂ becomes equal to the value of theintermediate signal S.

On the other hand, if the value of the intermediate signal S is lessthan the value of the voltage U₂, then the voltage at the controlterminal 127 of the executive element 107 will be closing the executiveelement 107, current I₀ through same decreases, resulting in thedecrease of the voltage U₂. This process will continue until the valueof the voltage U₂ becomes equal to the value of the intermediate signalS.

Hereby, due to the presence of feedback encompassing the executiveelement 107, the instrument resistor 105, and the subtractor 103, theratio

S≈U ₂  (4)

will always be abided in the proposed design, or, applying therespective values for S and U₂ from (2) and (3),

U _(C2) *U ₁ /U _(C1) =I ₀ *R  (5)

The ratio (4) performs stably from exposure to various destabilizingfactors, including wide range temperature variations, which is ensuredby the depth of the feedback.

By taking into consideration that the value of the resistance R₀ betweenthe high-potential, 110, and the low-potential, 112, terminals of theECR 1 is equal to the quotient of the voltage U₁ by the current I₀flowing through serially connected the executive element 107 and theinstrument resistor 105:

R _(O) =U ₁ /I ₀  (6),

-   -   -   -   the ratio (1): R_(O)=U_(C1)*R/U_(C2), can be derived                from (5) and (6).

It follows from that that by means of forming the intermediate signal atthe output of the voltage converter 101 as

S=U _(C1) *U ₁ /U _(C2),

further applying this signal to the first, non-inverting, input 117 ofthe subtractor 103, applying the voltage U₂=I₀*R across the instrumentresistor to the second, inverting, input 119 of the subtractor 103, andensuring the equality S≈U₂ due to the above-discussed feedback, thevalue of the resistance R₀ of the ECR 1 is made proportional to thepreferred value of the instrument resistor R connected in series withthe executive element, and the proportionality factor is equal to theratio of the value of the first controlling voltage to the value of thesecond controlling voltage.

Also following from the ratio (6) is the feasibility of obtaining smalland ultra-small values of R₀ at the sufficiently large I₀ provided bythe executive element.

Therefore, used to control resistance of a portion of an electriccircuit are variations of values of U_(C1) and/or U_(C2), whereby eithera directly proportional or an inversely proportional or a combinedfunction can be achieved depending on the requirements imposed on theECR.

The directly proportional dependence of the ECR from the controllingvoltage can be achieved if the value of U_(C2) is made fixed in anytechnically feasible way and only the value of U_(C1) is varied.

The inversely proportional dependence of the ECR from the controllingvoltage can be achieved if the value of U_(C1) is made fixed in anytechnically feasible way and only the value of U_(C2) is varied.

The combine function can be achieved where both U_(C1) and U_(C2) varyaccording to a preset rule.

The ECR 2 according to FIG. 2 (the second, digital, implementation)operates as follows.

Power supply voltage U_(CC) is applied to the terminals 202 and 208 ofthe electronically controllable resistor 2, whereas the first and seconddigital controlling voltages U_(C1-1) and U_(C2-1) are applied toterminals 204 and 206, respectively. Since the terminals 204 and 206 areconnected to terminals 209 and 211, respectively, the first and thesecond digital controlling voltages U_(C1-1) and U_(C2-1) come toterminals 209 and 211 of the voltage converter 201. At the same time,voltage U₁, corresponding to the potential difference between thehigh-potential, 10, and low-potential, 12, terminals of the ECR 2, isapplied from the high-potential terminal 10 to the third input 213 ofthe voltage converter 201.

Carried out in the analog-to-digital converter 233 of the voltageconverter 201 is conversion of the analog voltage U₁ into a digital formU₁₋₁ thereof. Resulting digital codes together with digital controllingvoltages U_(C1-1) and U_(C2-1) come to inputs of the digital computingunit 235 to be converted in such a way as to form an intermediate signalS₁ at respective outputs thereof. Just as in the implementation shown inFIG. 1, the value of the S₁ is equal to the product of the digital valueU₁₋₁ of the voltage at the high-potential terminal by the quotient ofthe value of the second controlling voltage by the value of the firstcontrolling voltage and is defined by the following ratio:

S ₁ =U ₁₋₁ *U _(C2-1) /U _(C1-1)  (7)

Alternatively, the voltage converter 201 can be made using amicroprocessor, as shown in FIG. 7. Designated in FIG. 7 are: aninput-output unit 701, an arithmetic-logical unit 702, a random-accessmemory 703, a read-only memory 704. As in FIG. 2, 233 is theanalog-to-digital converter and 237 is a digital-to-analog converter.

Made and designated in the above-mentioned manner, the voltage converter201 operates as follows.

The first, U_(C1-1), and the second, U_(C2-1), digital controllingvoltages come to inputs of the input-output unit 701. The voltage U₁from the high-potential terminal 10 of the ECR 2 (FIG. 2) comes to theinput 213 of the voltage converter 201 and then, after conversion intodigital form in the analog-to-digital converter 233, is also applied, asdigital voltage U₁₋₁, to the input-output unit 701. The input-outputunit 701 transfers the digital voltages U_(C1-1), U_(C2-1), and U₁₋₁ tothe arithmetic-logical unit 702 which, according to a program saved inthe read-only memory 704, calculates the intermediate signal S₁ indigital form

S ₁ =U ₁₋₁ *U _(C2-1) /U _(C1-1),

exchanging intermediate results of the calculations with therandom-access memory 703. From the arithmetic-logical unit 702, theobtained digital intermediate signal S₁ comes to the input-output unit701, and the latter transfers that signal to the inputs of thedigital-to-analog converter 237. The digital-to-analog converter 237transforms the digital signal S₁ into the analog form S thereof inaccordance with the relation (2).

Similar to the first, analog, implementation, the intermediate signal Sformed in the above-discussed way comes from the output 215 of thevoltage converter 201 to the first (non-inverting) input 117 of thesubtractor 103. Applied to the second (inverting) input 119 of thesubtractor 103 is voltage U₂ coming from the first terminal 121 of theinstrument resistor 105. The value of U₂ is equal to the voltage drop atthe instrument resistor 105 produced by current I₀ of the executiveelement 107. Due to the difference U₁ in potential between thehigh-potential terminal 10 and the low-potential terminal 12 of the ECR2, the current I₀ flows through the circuit comprising thehigh-potential terminal 10, the executive element 107, the instrumentresistor 105 connected in series with the latter, and the low-potentialterminal 12.

In the same manner that takes place in the implementation shown in FIG.1, value of U₂ can be expressed by the ratio

U ₂ =I ₀ *R,  (3),

where R is the preferred value of the instrument resistor, which can bechosen as small as engineering implementation allows.

The resulting voltage, which is proportional to the difference betweenthe intermediate signal S at the first (non-inverting) input 117 of thesubtractor 103 and voltage U₂ at the second (inverting) input 119 of thesubtractor 103, is applied from the output 123 of the subtractor 103 tothe control terminal 127 of the executive element 107. If the value ofthe intermediate signal S is larger than the value of the voltage U₂,then the voltage at the control terminal 127 of the executive element107 opens the executive element 107, the current I₀ through sameincreases, resulting in the increase of the voltage U₂. This processwill continue until the value of the voltage U₂ becomes equal to thevalue of the intermediate signal S.

If, on the other hand, the value of the intermediate signal S is lessthan the value of the voltage U₂, the voltage at the control terminal127 of the executive element 107 will be closing the executive element107, current I₀ therethrough decreases, resulting in the decrease of thevoltage U₂. This process will continue until the value of the voltage U₂becomes equal to the value of the intermediate signal S.

Hereby, due to the presence of feedback encompassing the executiveelement 107, the instrument resistor 105, and the subtractor 103, theratio

S≈U ₂  (4),

similar to the implementation illustrated by FIG. 1, will always beabided in the ECR 2 as shown in FIG. 2. Applying the respective valuesfor S and U₂ from (2) and (3),

U _(C2-1) ·U ₁ /U _(C1-1) =I ₀ ·R  (5)

Ensured by the depth of the feedback, the ratio (4) performs stably fromexposure to various destabilizing factors, including wide rangetemperature variations.When reasoning the same way as related to the version shown in FIG. 1,the ratio (1) again can be obtained:

R ₀ =U _(C1-1) ·R/U _(C2-1),

where the controlling voltages are presented in a digital form.

It follows from the above that when the voltage converter 201 comprisesan aggregation of the analog-digital converter, the digital computingunit, and the digital-to-analog converter, with the above-mentionedconnection between them, it becomes possible, similar to the variantshown in FIG. 1, to control resistance of the ECR, which resistance willbe proportional to the preferred value of the instrument resistorconnected in series with the executive element, and the proportionalityfactor will be equal to the ratio of the value of the first controllingvoltage to the value of the second controlling voltage.

Therefore, it is variations of values of U_(C1-1) and/or U_(C2-1) thatare used to control resistance of a portion of an electric circuit, tothereby achieve either a directly proportional function, or an inverselyproportional function, or a combined function depending on therequirements imposed on the ECR.

The directly proportional dependence of the ECR from the controllingvoltage can be achieved if the value of U_(C2-1) is made fixed in anytechnically feasible way and only the value of U_(C1-1) is varied.

The inversely proportional dependence of the ECR from the controllingvoltage can be achieved if the value of U_(C1-1) is made fixed in anytechnically feasible way and only the value of U_(C2-1) is varied.

The combine function can be achieved where both U_(C1-1) and U_(C2-1)vary according to a preset rule.

It follows from the above that the technical result ensured by theproposed ECR lies in widening the range of values of the preferredvalues of the resistance of the ECR, mainly to the side of small valuesthereof. While maintaining high tolerance to destabilizing factors, thevalue of the resistance of the portion of the electric circuit where theECR is placed can be as low as possible, with the technicalimplementation in view.

It is understood by those skilled the art that, when implementing theECR, various versions of the technical realization of the voltageconverter 101 can be used. For example, the multiplication and divisionoperations can be performed in an arbitrary order:

-   -   either performed first is the U₁*U_(C2) operation, and then the        result is divided by U_(C1); or    -   first performed is the U₁/U_(C1) operation, and then the result        is multiplied by U_(C2); or    -   the operation U_(C2)/U_(C1) is performed in the beginning        followed by multiplying the result by U₁;    -   or the operations U_(C1)*U₁/U₂ are performed in parallel, as,        for example, shown in        electronics.stackexchange.com/questions/325472/how-does-this-analog-op-amp-multiplier-divider-work.

The multiplication can be performed in many ways, for example asdisclosed in “Analog multipliers” (digteh.ru/Sxemoteh/mul/), Jan. 25,2014, or in “Analog signal multiplier”(electrono.ru/4-1-analogovyy-peremnozhitel-signalov-micrshema),

Specifically, commonly used are:

-   -   ring multipliers using bipolar transistors (IC AD530, AD534,        AD834, and many others);    -   pulse multipliers;    -   logarithmic multipliers;    -   variable slope multipliers, etc.

The division can also be implemented in many ways (for example, asdisclosed in “Analog signal divider” inelectrono.ru/4-1-analogovyy-peremnozhitel-signalov-micrshema):

-   -   by means of a conventional amplifier-inverter where a multiplier        is included in series with the feedback resistor;    -   using a variable-slope method;    -   using a method of taking logarithms, etc.

Where controlling signals come in a digital form, the voltage converter201 can be implemented using the digital computing unit, as discussed inthe above and illustrated by FIG. 2. In this case, the multiplicationand division can be performed by using software with any suitablemicroprocessor. Also, the multiplication and division can be performedby hardware, such as combinatorial multipliers/dividers or programmablelogic devices (PLD).

Those skilled in the art also understand that the executive element 107can include MOS- or bipolar transistors, or electronic tubes, etc.

All the other elements of the apparatus implementing the presentinvention are well-known and discussed in technical literature.

The above-discussed examples are not intended to limit the scope of thepresent invention.

For example, the range of the preferred values of the instrumentresistor can be chosen from several Ohm down to several milliohm.

To protect the executive element 107 (207) against transients, aparallel connection of an additional resistor R_(s) 337 (437) shown inFIG. 3 (FIG. 4) can be used. Terminals 333 (433) and 335 (435) of theresistor R_(s) are respectively connected to the terminals 129 and 125of the executive element 107.

The ECR illustrated by FIG. 1 can be made, for example, as a chip or achip assembly or a microplate, the terminals thereof being 102, 104,106, 108, 10, 12 (FIG. 1).

The ECR shown in FIG. 1 can also be made, for example, as a chip or achip assembly or a microplate, the terminals thereof being 102, 104,106, 108, 10, 12, 12, and 121, the executive element 107 being connectedby terminals 125, 127, 129 thereof to the terminals 121, 123, 10,respectively (FIG. 1).

The ECR presented in FIG. 2 can be made, for example, as a chip or achip assembly or a microplate, the terminals thereof being 202, 204,206, 208, 10, 12, and the terminals 204 and 206 can include groups ofterminals complying with serial interfaces or parallel interfaces, suchas I²C, SPI, increment-decrement.

The ECR depicted in FIG. 2 can also be made, for example, as a chip or achip assembly or a microplate, the terminals thereof being 202, 204,206, 208, 10, 12, 123, and 121, and the terminals 204 and 206 caninclude groups of terminals complying with serial interfaces or parallelinterfaces, such as I²C, SPI, increment-decrement, whereas the executiveelement 107 can be connected by the terminals 125, 127, 129 torespective terminals 121, 123, and 10.

Functionality of the present ECR is substantially wider than that of theprior art, because it makes it possible to realize mainly, but notlimited to, a low-ohmic ECR that can be used in the apparatuses where itis needed to control resistance both in direct dependence and inversedependence on the controlling voltage, as well as in dependence on bothvariable controlling voltages. With that, controlling resistance can beimplemented by using either analog controlling voltages or digitalcontrolling codes, whereas current flowing through the ECR can amount upto 10 A and more.

Battery charging devices, power factor correction devices for secondarypower supply units, synchronous motors, etc. are examples of suchapparatuses.

Therefore, the proposed solution is best-placed to be widely used invarious fields of electronics and electrical engineering for controllingresistance of a portion of an DC and AC electric circuit and, hence, forcontrolling voltage, current, and power of desired signals.

A real ECR was made according to the second option (using digitalschematics). It was tested at fixed values of U_(C2-1), whereas thefirst controlling voltage U_(C1-1) varied. FIG. 5 illustrates thedependence of resistance R₀ of the ECR from U_(C1-1). It shows that themeasured values of the resistance of the ECR, R_(0 meas) are in directproportion to the values of U_(C1-1) and highly linear, no matter whatvalues of U₁ are (for reference, calculated values, R_(0 calc), areshown as well). There, the values of R_(0 meas) are demonstrated in therange from 1.045 Ohm at U_(C1-1) equal to 0.02 V to 40 Ohm at U_(C1-1)equal to 0.85 V. No other apparatus known in the art and used forcontrolling resistance of a portion of an electric circuit ensures sosmall value of R₀.

It is understood that the examples provided do not limit the scope ofthe present invention. For example, hardware portions of some elementsdisclosed in the above can differ or partially coincide or completelycoincide with hardware portions of some other elements unless otherwiseis clearly indicated. Also, hardware portions of some elements can beplaced into various portions of some other elements unless otherwise isclearly indicated.

1. (canceled)
 2. An electronically controllable resistor (ECR) (1)comprising: a voltage converter (101), an instrument resistor (105), anda subtractor (103), the voltage converter (101) has a first, a second,and a third inputs (109, 111, 113), the first input (109) is connectedto a terminal (104) for connecting to a first control voltage source,and the third input (113) is connected to a high-potential voltageterminal (10), a first input (117) of the subtractor (103) is connectedto an output (115) of the voltage converter (103), a second input (119)of the subtractor (103) is connected to a first terminal (121) of theinstrument resistor (105), a second terminal of the instrument resistor(105) being connected to a low-potential terminal (12), wherein thesecond input (111) of the voltage converter (101) is connected to aterminal (106) for connecting to a second control voltage source, theECR (1) further comprises an executive element (107), a first terminal(125) of the executive element (107) is connected to the first terminal(121) of the instrument resistor (105), a second terminal (127) of theexecutive element (107) is connected to an output (123) of thesubtractor (103), and a third terminal (129) of the executive element(107) is connected to the high potential terminal (10), and wherein thevoltage converter (101) is adapted to multiply the voltage at thehigh-potential terminal (10) by the voltage at the second input (111)and to divide by the voltage at the first input (109), to produce anintermediate voltage signal at the output (115) of the voltage converter(101), whereby regulating the resistance of the ECR becomes available bythe subtractor (103) in the function of the difference between theintermediate voltage signal and the voltage drop on the instrumentalresistor (105) applied to the subtractor (103), which voltage drop iscreated by the current flowing through the instrumental resistor and theexecutive element.
 3. The ECR (1) as claimed in claim 2, wherein thevoltage converter (101) comprises three logarithmic amplifiers (601,602, 603), connected in parallel to each other, an adder (604), anadditional subtractor (605), and an exponential converter (606), whereinan input of the first logarithmic amplifier (603) is connected to thehigh-potential terminal (10) through the input (113) of the voltageconverter (101), the second logarithmic amplifier (602) is connected tothe input (111) of the voltage converter (101), the third logarithmicamplifier (601) is connected to the input (109) of the voltage converter(101), outputs of the first logarithmic amplifier (603) and of thesecond logarithmic amplifier (602) are connected to inputs of the adder(604), an output of the adder (604) is connected to a non-invertinginput of the additional subtractor (605), an output of the thirdlogarithmic amplifier (601) is connected to an inverting input of theadditional subtractor (605), an output of the additional subtractor(605) is connected to an input of the exponential converter (606), anoutput of the exponential converter (606) includes the output (115) ofthe voltage converter (101).
 4. The ECR (1) of claim 2, wherein thevoltage converter (101) comprises a digital computing unit (235), ananalog-to-digital converter (233), and a digital-to-analog converter(237), an input of the analog-to-digital converter (233) being connectedto the third input (113) of the voltage converter (101), an output ofthe analog-to-digital converter (233) being connected to an input of thedigital computing unit (235), a second input of the digital computingunit (235) being connected to the second input (111) of the voltageconverter (101), a third input of the digital computing unit (235) beingconnected to the first input (109) of the voltage converter (101), anoutput of the digital computing unit (235) being connected to an inputof the digital-to-analog converter (237), an output of thedigital-to-analog converter (237) including the output (115) of thevoltage converter (101), and wherein the first input (109) of thevoltage converter (101) is a digital bus, and wherein the second input(111) of the voltage converter (101) is also a digital bus.
 5. The ECR(1) of claim 2, wherein the executive element (107) includes at leastone FET, particularly a MOSFET.
 6. The ECR (1) of claim 2, wherein theexecutive element (107) includes at least one bipolar transistor,particularly an insulated-gate bipolar transistor.
 7. The ECR (1) ofclaim 2, wherein the executive element (107) includes at least onevacuum tube
 8. A circuit for controlling the ECR (1), the circuitcomprising a voltage converter (101) and a subtractor (103), the voltageconverter (101) having first, second and third inputs (109, 111, 113),the first input (109) is for connecting to a source of a first controlvoltage, and the third input (113) is for connecting to a high-potentialvoltage terminal (10) of the ECR (1), a first input (117) of thesubtractor (103) is connected to an output (115) of the voltageconverter (103), a second input (119) of the subtractor (103) is forconnecting to a first terminal (121) of an instrument resistor (105) ofthe ECR (1), wherein the second input (111) of the voltage converter(101) is for connecting to a source of a second control voltage, anoutput (123) of the subtractor (103) is for connecting to a controlinput of an executive element of the ECR (1); and wherein the voltageconverter (101) is adapted to multiply the voltage at the high-potentialterminal (10) of the ECR (1) by the voltage at the second input (111)and to divide by the voltage at the first input (109), to produce anintermediate voltage signal at the output (115) of the voltage converter(101), whereby regulating the resistance of the ECR (1) becomesavailable by the subtractor (103) in the function of the differencebetween the intermediate voltage signal and the voltage drop on theinstrumental resistor (105) of the ECR (1) applied to the subtractor(103), which voltage drop is created by the current flowing through theinstrumental resistor (105) and the executive element (107) of the ECR(1).
 9. The circuit of claim 8 for controlling the ECR (1), wherein thevoltage converter (101) includes three logarithmic amplifiers (601, 602,603), connected in parallel to each other, an adder (604), an additionalsubtractor (605), and an exponential converter (606), wherein an inputof the first logarithmic amplifier (603) is for connecting to thehigh-potential terminal (10) through the input (113) of the voltageconverter (101), an input of the second logarithmic amplifier (602) isconnected to the input (111) of the voltage converter (101), an input ofthe third logarithmic amplifier (601) is connected to the input (109) ofthe voltage converter (101), outputs of the first logarithmic amplifier(603) and of the second logarithmic amplifier (602) are connected toinputs of the adder (604), an output of the adder (604) is connected toa non-inverting input of the additional subtractor (605), an output ofthe third logarithmic amplifier (601) is connected to an inverting inputof the additional subtractor (605), an output of the additionalsubtractor (605) is connected to an input of the exponential converter(606), an output of the exponential converter (606) including the output(115) of the voltage converter (101).
 10. The circuit of claim 8 forcontrolling the ECR (1), wherein the voltage converter (101) comprises adigital computing unit (235), an analog-to-digital converter (233), anda digital-to-analog converter (237), an input of the analog-to-digitalconverter (233) being connected to the third input (113) of the voltageconverter (101), a first input of the digital computing unit (235) beingconnected to an output of the analog-to-digital converter (233), asecond input of the digital computing unit (235) being connected to thesecond input (111) of the voltage converter (101), a third input of thedigital computing unit (235) being connected to the first input (109) ofthe voltage converter (101), an input of the digital-to-analog converter(237) being connected to an output of the digital computing unit (235),an output of the digital-to-analog converter (237) including the output(115) of the voltage converter (101), and wherein the first input (109)of the voltage converter (101) is a digital bus, and wherein the secondinput (111) of the voltage converter (101) is also a digital bus.